Question: Find the curve defined by the equation
\[\theta = \frac{\pi}{3}.\](A) Line
(B) Circle
(C) Parabola
(D) Ellipse
(E) Hyperbola

Enter the letter of the correct option.
Explanation: All points that make an angle of $\frac{\pi}{3}$ with the positive $x$-axis lie on the graph.

[asy]
unitsize(1 cm);

draw(3*dir(240)--3*dir(60),red);
draw((-2,0)--(2,0));
draw((0,-3)--(0,3));

label("$\frac{\pi}{3}$", (0.5,0.4));
label("$\theta = \frac{\pi}{3}$", (2,1.8), red);
[/asy]

But all points that make an angle of $\frac{\pi}{3} + \pi$ with the positive $x$-axis also lie on the graph, since the radius $r$ can be negative.  Thus, the graph is a line.  The answer is $\boxed{\text{(A)}}.$